昨天的Textfield我們其實也可以改成這樣：

 @IBAction func changePageAction(_ sender: Any) {
        
        
        let AlertController = UIAlertController(title: "切換頁面？", message: "按下OK後跳轉", preferredStyle: .alert)
        
        func option(optionTitle: String, optionStyle: UIAlertAction.Style ,mergehandler: ((UIAlertAction) -> Void)?) {
            AlertController.addAction(UIAlertAction(title: optionTitle, style: optionStyle, handler: mergehandler))
        }
        option(optionTitle: "2" , optionStyle: UIAlertAction.Style.default, mergehandler: { action in
            
            let switchToSecondScreen = SecondFrame()
            self.navigationController?.pushViewController(switchToSecondScreen, animated: true)
            
        })
        option(optionTitle: "3" , optionStyle: UIAlertAction.Style.default, mergehandler: { action in
            
            let switchToThirdScreen = ThirdFrame()
            self.navigationController?.pushViewController(switchToThirdScreen, animated: true)
            
        })
        option(optionTitle: "取消" , optionStyle: UIAlertAction.Style.destructive, mergehandler: { action in
            
        })
        
        present(AlertController, animated: true, completion: nil)

當然我們也可以用輸入框的方式做：

@IBAction func changePageAction(_ sender: Any) {
    
        let CancelAlertController = UIAlertController(title: "轉換頁面失敗", message: "請重試！", preferredStyle: .alert)
        
        let AlertController = UIAlertController(title: "切換頁面？", message: "輸入你要跳轉的頁數", preferredStyle: .alert)
        
        AlertController.addTextField { textField in
            
            textField.placeholder = "page?"
            
        }
        
        let alerOktAction = UIAlertAction(title: "ok", style: .default) {[unowned AlertController] _ in
            
            let page = AlertController.textFields?[0].text
            
            switch page {
            
            case "2":
                let switchToSecondScreen = SecondFrame()
                self.navigationController?.pushViewController(switchToSecondScreen, animated: true)
                
            case "3" :
                let switchToThirdScreen = ThirdFrame()
                self.navigationController?.pushViewController(switchToThirdScreen, animated: true)
                
            default:
                self.present(CancelAlertController, animated: true, completion: nil)
            }
        }
        
        let TryagainAlertAction = UIAlertAction(title: "OK", style: .destructive, handler: nil)
        
        let alertCancelAction = UIAlertAction(title: "Cancel", style: .destructive, handler: nil)
        
        AlertController.addAction(alerOktAction)
        
        AlertController.addAction(alertCancelAction)
        
        CancelAlertController.addAction(TryagainAlertAction)
        
        present(AlertController, animated: true, completion: nil)
        
    }
    
}

成果：